Leakage current, or photo current, in a semiconductor circuit is often the result of exposure to a high level burst of ionizing radiation. The leakage current causes a reduction in the supply voltage, also referred to as rail span collapse, which may in turn cause unpredictable behavior in circuit performance. For example, data stored in registers and latches may become corrupt. In particular, cache memory, integrated circuits with on-chip memory, or other memory arrays can be significant sources of leakage current for a computer system. The memory arrays are implemented in memory devices such as SRAMs, DRAMs, and ROMs that are widely used in electronic circuits.
Semiconductor circuit engineers have attempted to resolve the leakage current problem by designing improved transistor structures, improved manufacturing methods, or devising ways to detect transient dose conditions. However, these designs and methods entail fundamental changes in the transistor structure and manufacturing methods, for example, and therefore may require expensive retooling and/or reconfiguration.
Low power consumption in memory devices has always been a goal of semiconductor circuit engineers. Even when a memory array is inactive, power is still being consumed because of leakage currents. The effects of leakage currents become more pronounced as transistor threshold voltages are decreased in low supply voltage applications. Reduced power consumption is especially important in those circuit applications that use portable power supplies, such as consumer electronic products. Furthermore, as the size of memory in systems multiplies, the power consumed by the memory during standby becomes increasingly significant.
Accordingly, there arises a desire to reduce leakage current and power consumption in memory devices and improve its performance.